In control panels such as heating and air conditioning control heads or radio control heads it is common practice to mount switches, potentiometers and other devices having control shafts or levers in a housing with the shafts or levers protruding through a front panel. A knob fits on the end of each shaft or lever and is securely retained by a spring which fits within a bore in the knob and surrounds the shaft or lever. Typically the shaft and knob bore are D-shaped and the conforming spring is called a D-spring. Usually a detent mechanism is provided to give a feel of knob position for identifying unique locations or increments of movement. For example, a single indentation may be used to mark the center or neutral position of a control, or a series of teeth may determine incremental movement of the control.
The detent may comprise, for example, a toothed or otherwise indented wheel fixed to the shaft for rotation therewith, also secured by a D-spring, and a spring biased ball supported on a structure adjacent the shaft and pressed into engagement with the teeth or indentations of the wheel. Such an elaborate mechanism is expensive and difficult to assemble due to the large number of parts. A specific example is shown in FIG. 1. A control mechanism of a known type employs a switch 10 having a control shaft 12 of D-shaped cross-section and a mounting bracket 14 for attachment to a front panel or other housing member, not shown. The bracket 14 has a pair of spaced ears 16 which retain a leaf spring 18. A toothed detent wheel 20 defines a series of peripheral indentations and has a D-shaped bore 22 which fits over the shaft 12 against the bracket 14. A D-spring 24 between the shaft 12 and the bore 22 retains the wheel 20 in place. A detent ball 26 is urged against the toothed edge of the detent wheel 20 by the leaf spring 18. This entire sub-assembly fits within a housing with the end of the control shaft 12 extending outwardly through the front panel, not shown. A knob 28, also having a D-shaped bore, not shown, fits over the end of shaft 12 and is retained by another D-spring 30. In operation, as the knob 28 and shaft 12 are turned, the detent wheel 20 also turns causing the ball 26 to ride up and down in the toothed periphery, so that the detent feel is transmitted to the knob and, when the knob is released, the ball 26 will remain seated in an indentation to establish a discrete control shaft position. In the interests of economy and reliability it is desirable to simplify the detent apparatus.